This invention relates to a surgical method. More particularly, this invention relates to a method for selectively excising tissue during a surgical procedure. This invention also pertains to an ultrasonic surgical blade utilizable in performing the method.
Over the past 30 years, several ultrasonic tools have been invented which can be used to ablate or cut tissue in surgery. Wuchinich et al. in U.S. Pat. No. 4,223,676 and Idemoto et al in U.S. Pat. No. 5,188,102 disclose such devices.
Ultrasonic surgical devices generally fall into two categories. One is a blunt tip hollow probe that vibrates at frequencies between 20 kc and 100 kc, with amplitudes up to 300 microns or more. Such devices ablate tissue by either producing cavitation bubbles which implode and disrupt cells, tissue compression and relaxation stresses (sometimes called the jackhammer effect) or by other forces such as microstreaming of bubbles in the tissue matrix. The effect is that the tissue becomes liquefied and separated. It then becomes emulsified with the irrigant solution. The resulting emulsion is then aspirated from the site. Bulk excision of tissue is possible by applying the energy around and under unwanted tumors to separate it from the surrounding structure. The surgeon can then lift the tissue out using common tools such as forceps.
A second kind of ultrasonic device uses a sharp blade instead of a blunt hollow probe. Here a cutting action takes place. Such a sharp ultrasonic blade is the subject of U.S. Pat. No. 6,379,371. As disclosed therein, the blade shape is semicircular at the distal portion with two straight sides parallel to the longitudinal axis and extending back to the shoulder that contacts the vibrating probe. Male threads are shown which mate with the female threaded socket of the probe (or transducer) to allow tight intimate contact of the probe and blade tip shoulder. When the two are torqued together, they form a single resonant body that will vibrate in sympathy with the transducer and generator combination. The distal end of the blade will vibrate with an amplitude set by the mechanical gain of the probe/tip geometry and the input amplitude provided by the transducer generator combination. This motion provided the cutting action for the tissue in question.
The blade of U.S. Pat. No. 6,379,371 was intended for the cutting or excising of bone or similarly hard tissue in surgical applications. In tests conducted in vitro and in vivo, it was noted that the blade, when sharp, cut both hard and soft tissue with similar ease. In delicate operations, such as sinus lift surgery or craniotomies where the goal is to cut an aperture in the front of the skull to expose sinus tissue or brain but not cut the membrane directly beneath the bony structure, this is very important. It is also important in spinal and brain surgery where bone tissue must be cut with a minimum of damage to underlying soft tissues such as the dura mater. It was noted in early in vitro testing that the blade, as it plunged through the cortex of the bone punctured the membrane or ripped it. After some experience, competent surgeons were able to master the technique, but the learning curve was steep.
A sharp blade such as that of U.S. Pat. No. 6,379,371 has been shown in both in vitro and in vivo testing to be an effective tool for cutting bone, cartilage, soft tissues such as vein, arteries and can even be used to cut skin with minimal secondary trauma. In this kind of blade, ablation is not the primary cause but a shearing or cutting action predominates.
Both the ablating instrument and the cutting or incising instrument have limitations when used as surgical tools. The blunt probe is effective in ablating or excising soft liquid rich tissues such as fat, liver or spleen, but less effective or even non-effective in dry, hard material such as hard cartilage or bone. The blade type devices are effective in the hard material but also are not soft tissue sparing so that collateral tissue damage is incurred, rendering the blade undesirable around nerve clusters or other important structures. Because sharp blades tend to cut everything, tissue selectivity is reduced to nil and no differentiation may be made between hard and soft material.
In certain applications, such as sinus cavity lifts and maxialfacial surgery such as third molar extraction, a tool would be useful which could cut the harder bony material with less trauma while sparing the soft tissues underneath if they were inadvertently touched by the vibrating blade.